1. Field of the Invention
This invention relates to 3-R.sup.1 -3-oxoprop-1-ene-1,1-di-phosphonic acids and salts thereof, to a process for their production, to their use as thresholders, and to complexing composition containing them.
2. Statement of Related Art
1-amino-1,1-diphosphonic acids corresponding to the following general formula ##STR3## in which A, B and C represent aliphatic, cycloaliphatic or aromatic hydrocarbon radicals, in addition to which B and C can also represent a hydrogen atom, are known from the prior art. They are prepared by reaction of nitriles with phosphorus trihalides and subsequent hydrolysis or alcoholysis (German application No. 10 02 335), reaction of nitriles with phosphorous acid (German application No. 26 25 767) or reaction of carboxylic acid amides with phosphorus trihalides in the presence of phosphorous acid and subsequent hydrolysis (German application No. 19 58 123). Phosphonic acids corresponding to general formula (I) above have the ability to complex heavy metal ions and alkaline earth metal ions. Accordingly, they are widely used as complexing agents or chelating agents in the softening of water, in detergent manufacture, in the textile field and in papermaking.
It is known from German application No. 16 17 729 that 1-hydroxyethane-1,1-diphosphonic acid can be used as a complexing agent for inhibiting the formation of tartar.
In addition, structurally related compounds corresponding to the following general formula ##STR4## are known as complexing agents. In formula (II), B and C represent hydrogen or aliphatic or aromatic radicals in analogy to general formula (I) above, while D is a C.sub.1 -C.sub.5 alkylene radical. German application No. 34 34 667 and German patent No. 25 34 391 describe the use of compounds corresponding to general formula (II) and water-soluble salts thereof as complexing agents for alkaline earth metal ions, preferably calcium ions, and as thresholders.
U.S. Pat. No. 2,026,078 describes the synthesis of ethylene-1,1-diphosphonic acid and its use as a complexing agent for heavy metals.